The type VI secretion system: a tubular story

Abstract

The molecular mechanism by which proteins are secreted in gram-negative bacteria is supported by nanomachines called type I to type VI secretion systems (T1SS to T6SS). Previous data suggested that the ClpV ATPase energizes the transport of Hcp and VgrG proteins through the T6SS secretion channel. The identification of a yet unknown tubular structure, which interacts with ClpV, adds another level of complexity and challenges our vision of the T6SS working model.

Figure 1

Schematic representation of the T6SS. (A) Model in which Hcp (yellow) and VgrG (green) are secreted through the yet uncharacterized T6SS secreton (dark grey and question marks). The first step in the secretion process is the threading of Hcp and VgrG through the central channel of the hexameric ClpV ATPase (orange). (B) In this panel, the ClpV ATPase is shown involved in the severing of VipA (red)/VipB (blue) tubules, by threading smaller VipA/VipB complexes through the ClpV pore. In this context, it is not understood how this process and the T6SS-dependent secretion of Hcp and VgrG could be linked (bidirectional arrow and question marks).